TILLAGE EFFECTS ON SELECTED CHEMICAL-PROPERTIES OF GRANTSBURG SILT LOAM

The objective of this research was to determine the effects of tillage systems on selected chemical properties of a sloping and eroded soil which had previously been in sod. A tillage project was initiated in the spring, 1989 in southern Illinois on a soil with a root-restricting fragipan. Com (Zea mays L.) and soybean [Glycine max (L.) Merr.] were grown on the plot area on a yearly rotation system. Prior to the application of lime or tillage treatments the 0-15 cm Ap horizon had a pH of 6.3, organic carbon (C) of 1.4 g/100 g, and CEC equal to 17 meq/100 g. Lime had been surface applied early in the spring of 1989 prior to moldboard (MP) and chisel (CP) plowing. Moldboard plowing had lower pH than the other treatments in the 0-5 cm layer in 1989 due to the moldboard plow mixing low pH subsoil material into the 0-5 cm layer and mixing surface applied lime into the 5-15 cm layer. During the 4th year, organic C was lowest for MP (1.28 g/100 g) and highest for no tillage (NT) (1.65 g/100 g), with CP having organic C content of 1.52 g/100 g in the 0-5 cm layer. The differences in organic C were attributed to the effects of incorporation of plant residues below the 0-5 cm layer in the moldboard and chisel plow treatments. Effects of tillage on organic C content were not significant in the 5-15 cm layer. Soil phosphorus (P) (Bray Pl) and extractable potassium (K) were stratified, with the largest amounts of these two elements found within the top 5 cm of soil. In general, tillage did not have any significant (P=0.05) effect on either extractable calcium (Ca) or magnesium (Mg). Differences were observed in exchangeable ammonium-nitrogen (NH4+-N) and nitrate-nitrogen (NO3--N) by tillage treatments and were affected by soil moisture content and previous crop residues. Cation exchange capacity (CEC) was lower for MP at the 0-5 cm layer as compared to NT and CP in the 3rd year. At the 5-15 cm layer CEC was lower for NT as compared to CP and MP. The differences in CEC were attributed to the observed differences in organic C and possibly the effects of moldboard and chisel plow mixing subsoil materials slightly higher in clay content into the Ap horizon. In 1989, com grain yield for NT was significantly lower than MP and CP. In 1990, 1991 and 1992 the crop yields by tillage treatment were not significantly different. Any conversion of conservation reserve land from sod into NT corn and soybean production could experience similar management problems and corn yield reductions the first year. The initial yield advantage MP system had the 1st year did not occur the last three years. Based on four years of observation, no-till and chisel plow systems may better maintain long-term productivity of sloping soils than moldboard plow systems because of changes in distribution and availability of nutrients and organic C in the 0-5 cm layer, reduced soil erosion, and yield trends.